A number of devices for parenteral injection have been developed, which are intended to contain a plurality of doses of a pharmaceutical agent which are to be administered successively with appropriate intervals such devices have turned out to be very suitable in those cases when the patient has to administer the doses to himself, such as in the treatment of diabetes with insulin.
Injection devices of this type are often arranged to utilize an injection ampoule, which may be of the single-chamber or dual-chamber type. In preparing the device for injection, the user inserts the ampoule in the device and, in the case of a dual-chamber ampoule, carries out the necessary mixing of the contents of the two chambers. After this, the ampoule is connected to an injection needle, and a dose of the pharmaceutic agent is administered. The amount of the dose is determined by a suitable mechanism, often by controlling the stroke of the plunger in the injection ampoule. When the appropriate number of doses have been administered, the injection ampoule is removed and discarded, and a new ampoule may then be inserted.
As different patients require different doses of a pharmaceutical agent, it is necessary to use multi-dose injection devices where the dosage can be varied and the agent can be utilized with as little waste as possible. This is of special importance when very expensive agents are administered, such as certain hormones and proteins. If only one dose could be administered from each injection ampoule and the rest would go to waste, the cost of the treatment would be prohibitively high.
However, there exists a serious problem in the use of multi-dose injection devices. As the contents of the injection ampoule will get into some contact with the outside environment once the seal of the ampoule has been broken at the first administration, there is a certain risk for a contamination of the contents of the ampoule by microorganisms and viruses. This problem is aggravated by the fact that a new injection needle is usually connected to the device for each new administration.
It is of course necessary that sterility is maintained in the pharmaceutical agent during the whole period when it is present in the device and doses of the agent are drawn off to be administered. This object has usually been attained by the addition of preserving agents to the agent in the injection ampoule, such as methyl or propyl paraben and the like. The addition of such preserving agents, however, is not always acceptable, as they may have a detrimental effect on the pharmaceutic agent used. This is of special importance when very sensitive agents are used, such as those which have to be packed in a dual-chamber ampoule because of their sensitivity to harmful influences. For such pharmaceutical agents, the presence of preserving agents cannot usually be accepted.
The presence of preserving agents would not be necessary if each single dose of the pharmaceutic agent could be kept in a chamber separate from the other doses and would not get into contact with the outside environment until immediately before the administering of the agent. At the same time, it should be possible to arrange these chambers such that each of them contains the desired amount for the dose.
A further object of the invention is to arrange for two or more components of the pharmaceutic agent to be kept separate initially, and to mix said components before said chambers are arranged. These objects are attained by the present invention.